1. Field of the Invention
The invention relates in general to a method for determining restored position, and more particular, to a restoration method to avoid missing line and image repetition.
2. Related Art of the Invention
Due to advancing and fast-developing electronic techniques, the electronic industry has become one of the most important industries in modern society. Many high performance calculating systems are consequently being produced, and more and more electronic products are being used in daily life. In recent years, the growing processing speed and data storage capacity of the processor has greatly enhanced the performance of image processing, while the image processor such as the optical scanner or digital camera have become widely applied.
In the current operating process of the scanner, the graphic data generating speed is far faster than the data transmission speed between the scanner and the host, and therefore the graphic data scanned by the scanner requires a place for temporary storage. Such place for temporary storage is called a buffer, which ranges between about 32 Kbytes to about 512 Kbytes.
The faster the graphic data is generated; the more graphic data is stored in the buffer. When the buffer is full of the graphic data, the scanner has to stop scanning. If the scan continues under such circumstances, the graphic data will be lost, or operation problems may occur.
When the scanner head is performing scanning, the scanning process has to be stopped if the buffer is filled with the graphic data. Generally speaking, the stopped position is called the restored position. To allow each area of the document to have the same exposure time, the scanner head has a constant speed during scanning. Thus, the scanner head has to move backward with a certain distance. When the is completely emptied, the scanner head proceeds to the previously stopped position, that is, the restored position, to continue scanning. The scanning speed has to reach the previous scanning speed to result in a stable performance.
The procedure from filling the buffer with the graphic data, stopping scanning, the scanner head moving backward and restoring to the restored position and starting scanning is called smearing.
The smearing procedure is normally determined by the low transmission speed of interface connected to the host, such as the SCSI, USB and EPP. Alternatively, it also occurs when the computer host is too busy with other operation processes to read data from the interface. As a result, the graphic data is accumulated in the buffer until it is completely filled to cause smearing.
In the above smearing procedure, while returning to the restored position after moving backward, the scanner head may not return to the exact restored position due to the inertia effect or mechanic error of the scanner; therefore missing line and repetition of graphic data may occur.